Contorno de proa

gums and β-glucans were used to create viscous solutions, while viscosity changes from adding inulin were minimal (Borderías and others 2005).

2.2.4 PHYSIOLOGICAL EFFECTS  

  Dietary fiber is categorized into two categories, soluble and insoluble, and yet the types of fibers that fall into either category have different positive effects on the human body, to differing degrees (Caballero and others 2005). As mentioned earlier, dietary fiber is not digested by the enzymes in the human body, but to a certain extent it is fermented by the gut micro flora.

As described in the Encyclopedia of Human Nutrition (Food and Nutrition Board 2005.), food products that contain fiber have a longer transit time in the stomach, because of the body’s necessity to break down the product into smaller particles. The example given was a raw apple versus apple juice, stating that rigorous muscle activity is required to breakdown a raw apple and thus slows the rate of absorption of glucose into the blood stream (occurring in the small intestine). It was also stated that, soluble fibers like guar gum, pectin and β-glucan increase total transit time from mouth to cecum.

2.2.4.1 CARDIOVASCULAR DISEASE  

  Cardiovascular disease (CVD) was the leading cause of death in the United States in 2011, followed by cancer (Centers for Disease Control and Prevention). The

American Heart Association reported a 32.7% decrease in deaths attributed to CVD from 1999-2009, although 1 in every 3 deaths were related to CVD (Go and others 2013).

Greater than 2150 American deaths per day are due to CVD (Go and others 2013) . The four most common types of CVD are coronary heart disease, heart failure, stroke, and high blood pressure.

  Risk factors for CVD include high cholesterol, glucose, and blood pressure. It has been estimated that 31.9 million adults aged 20 and over have a total serum cholesterol level of 240mg/dL or greater (Go and others 2013).

According to the American Heart Association, Coronary Heart Disease (CHD) is a term for the buildup of plaque in the coronary arteries, which is a risk factor for a myocardial infarction (Heart Attack). Risk factors for developing CHD are high Low Density Lipoprotein cholesterol (LDL), low High Density Lipoprotein (HDL)

cholesterol, high blood pressure, diabetes, smoking, family history, being a

post-menopausal woman or a man over the age of 45, and possibly obesity (Wilson and others 1998; Go and others 2013).

Dietary fiber has been documented as decreasing the risk of developing CHD. It has been noted that it is sometimes hard to verify if it is the fiber that is decreasing the risk or other components in the diet associated with a high fiber intake (Wilson 2010).

Soluble dietary fiber has been shown to decrease the risk, rather than the insoluble form.

The role of fiber in lowering the risk of CHD, is through lowering of LDL cholesterol,

are several proposed mechanisms for lowering of cholesterol by dietary fiber (Bourdon and others 1999):

1) Dietary fiber binds to bile acids, thus cholesterol is carried from the body 2) Inhibition of liver synthesis of cholesterol by propionate, a short chain fatty

acid (SCFA) which is produced by fermentation of dietary fiber by colonic bacteria.

3) Inhibition of liver synthesis of cholesterol by lower levels of insulin

MECHANISM 1

The food containing soluble fiber is masticated in the mouth, swallowed, and then churned into chyme in the stomach with a pH of about 3. The chyme is then released through the lower pyloric sphincter into the duodenum where the pancreas excretes bile into the chyme, to increase the pH. The viscous gel created by the soluble fiber captures the bile acids, and therefore does not allow for re-absorption in the ileum. The bile is then excreted in the feces. Bile is synthesized from cholesterol by the liver. The liver has two ways of obtaining cholesterol, 1) from blood, 2) from re-absorption in the ileum. If the bile acids are being excreted in the feces rather than absorbed in the ileum, then the liver must obtain cholesterol from the blood. This is the proposed mechanism for lowering blood cholesterol (Bourdon and others 1999).

MECHANISM 2

A second proposed mechanism for lowering cholesterol is a by-product of soluble fiber fermentation by bacteria in the large intestine. When fiber is fermented, this produces short chain fatty acids (SCFA), one of which is propionate, which can inhibit synthesis of cholesterol. In the proximal colon, carbohydrates are fermented to SCFA’s, hydrogen and carbon dioxide (Choque Delgado and others 2011). The SCFA’s produced are acetate, propionate, and butyrate. Acetate is used by the liver as the sole precursor for cholesterol synthesis, propionate is used to both facilitate and inhibit gluconeogenesis, as well as inhibit cholesterol synthesis (Choque Delgado and others 2011). Butyrate is used as fuel for colonocytes, and helps to treat gut inflammation, and possibly cancer.

A study concluded, that the cholesterol lowering effect of SCFA’s is the ratio of acetate to propionate (Wong and others 2006). While rectal infusions of acetate alone increased serum LDL, a mixture of 180 mmol of acetate and 60 mmol of propionate, showed a lower serum cholesterol (Margareta and Nyman 2003). While the acetate promoted cholesterogenesis, it appeared that propionate negated the effect of acetate.

  Basic cholesterol synthesis is as follows:

Acetate →³Acetyl-CoA→⁴HMG-CoA→⁵Mevalonate→

3 Acetyl‐CoA reductase 

4 HMG‐CoA Synthase 

Mevalonate pyrophosphate→Isopentenyl pyrophosphate→Dimethylallyl

pyrophosphate→ Geranyl pyrophosphate → Farnesyl pyrophosphate→ Squalene→

Cholesterol

HMG-CoA Reductase is the rate limiting enzyme of cholesterol biosynthesis.

Propionate inhibits hepatic cholesterol synthesis by possibly reducing the activity of HMG-CoA Reductase (Theuwissen and Mensink 2008). While inhibiting the enzymes that catalyze the synthesis of cholesterol is thought to be a good mechanism, it is hard to verify whether this mechanism is the one causing the reduction in serum cholesterol levels. Several studies have been done to test the cholesterol lowering capability of propionate, and yet have been inconclusive (Nishina and Freedland 1990; Topping and Clifton 2001; Levrat and others 1994; Strugala and others 2003).

MECHANISM 3

Insulin activates HMG-CoA Reductase (HMG-Co AR), so when a high glycemic load is consumed, blood glucose rises, insulin levels increase and this activates HMG-Co AR, which increases hepatic cholesterol synthesis (Gunness and Gidley 2010). When viscous soluble dietary fiber is consumed, digestion of macronutrients is slowed by delaying gastric emptying and decreasing glucose absorption (Queenan and others 2007;

Bourdon and others 1999). With a low glycemic response, insulin levels remain low, which could cause an inhibition of HMG-Co AR, and reduce hepatic cholesterol synthesis (Lundin and others 2004).

While each of the proposed mechanisms above may decrease serum cholesterol, according to (Bourdon and others 1999), the only mechanism that is measurable is that viscous fiber traps the bile salts and they are excreted in the feces. The effects of

propionate have not been thoroughly established, and the effect of insulin is complex, so it is hard to test the specific result on serum cholesterol (Bourdon and others 1999). The viscous nature of soluble dietary fiber is the property that is thought to be the greatest factor associated with decreased levels of serum cholesterol (Topping and Cobiac 2005).

Soluble and insoluble fibers used together have the greatest benefit to the host.

The insoluble fiber decreases gut transit time, thus more of the bile acids are excreted rather than reabsorbed, and the by-products of the fermentation of soluble fiber, such as acetate, are not reabsorbed either. Both of these factors together have the greatest

potential to lower serum LDL-C (Brownlee 2011; Elleuch and others 2011; Topping and Cobiac 2005).   

2.2.4.2 DIABETES  

  Fiber has been investigated for possibly protecting against diabetes. Fiber has been shown to reduce glycemic response in several studies with 33 out of 50 studies that used viscous fibers, and 3 out of 14 in studies using nonviscous fibers (Food and

Nutrition Board 2005.). The proposed mechanisms are 1) delay of glucose uptake and 2) attenuation of insulin response. These mechanisms were supported by The Zutphen

glycemic load, and low in cereal fiber lead to increased risk and were up to 2.5 times more likely to develop diabetes than subjects who consumed a diet with a low glycemic load and a high intake of cereal fiber (Food and Nutrition Board 2005.). Dietary fiber may slow the digestion of starch which would slow the absorption of glucose and thereby reduce the insulin “response” (Topping and Cobiac 2005). As stated above, viscous fibers tended to have greater effect on insulin response than did non-viscous fibers, and it has been proposed that the viscosity may be part of the reason for the positive effect. The glucose may get trapped in the gel network in the gut lumen and thus be inaccessible to the villi to be absorbed (Topping and Cobiac 2005).

2.2.4.3 OBESITY  

  Results have differed with respect to whether fiber has any positive effect on weight maintenance or weight loss. Fiber is said to give the subject the feeling of fullness (satiety) when the meal is of low caloric value, and is supplemented with fiber. It is believed that this feeling of fullness will result in less caloric intake and thereby help with weight loss. However, the intake of fiber varied, and the greatest effect was seen with a high intake of 30+ grams a day (Food and Nutrition Board 2005.). Therefore, while there is correlation between subjects with high fiber intake, and having a low BMI (Davis and others 2010), there is very little correlation between high fiber intake and weight loss.   

2.2.4.4 CANCER  

Studies have been conducted on the possibility of dietary fiber reducing the risk of colorectal cancers. The results of some of the studies have been inconclusive, and it was suggested that the reason for this was the different analytical methods used in the different studies (Topping and Cobiac 2005). It was also concluded that 1) timing of the intervention, 2) confounding role of other dietary factors and 3) individuals may not consume sufficient quantity of fiber or the right type of fiber (Food and Nutrition Board 2005.). Yet mechanisms have been put forth by which dietary fiber may reduce the risk of developing cancer (Topping and Cobiac 2005; Food and Nutrition Board 2005.).

1) Increased stool bulk, mostly by insoluble dietary fiber. This decreases the gut transit time, thereby reducing contact with carcinogens.

2) Binding of bile acids thereby lowering concentration of mutagens

3) Modifying gut microbiota which lowers colonic ammonia by fixing nitrogen in the bacterial mass.

4) Production of short chain fatty acids which lower colonic pH, thereby decreasing absorption of toxic alkaline compounds. Also, butyrate is a preferred substrate of colonocytes (Roediger 1982) and promotes normal cell phenotype, and slows cancer cell growth.

2.2.4.5 PREBIOTIC 

Fiber can also function as a prebiotic. A prebiotic is defined as: a non digestible food ingredient that is beneficial to the host by selectively stimulating growth or activity of one or a number of colonic bacteria, and in so doing improves host health (Gibson and Roberfroid 1995). Gibson and Roberfroid also list four criteria that a food ingredient must meet to be considered a prebiotic: 1) It must not be hydrolyzed or absorbed in the upper part of the gastrointestinal system; 2) It must be a selective substrate of beneficial bacteria in the colon; 3) It promotes the growth of healthy bacteria, thereby modifying the colonic bacteria; 4) It stimulates the lumen of the gut and large intestine to produce end products that are absorbed into the blood that are beneficial to health.

According to (Gibson and Roberfroid 1995), fructooligosaccharides are considered a prebiotic. However, while some carbohydrates are classified as “Colonic Food,” this does not necessarily result in being classified as a prebiotic.

2.3 INULIN  

Inulin is a non-digestible fructooligosaccharide (FOS) which is defined as a chain of fructose units with a terminal glucose unit (Toneli and others 2010). While many vegetables contain inulin, the chicory root and Jerusalem artichoke are the sources used for commercial production (Toneli and others 2010). The dry matter of chicory root is approximately 14.5 percent inulin (Milala and others 2009). The dry matter of Jerusalem

artichoke is between 16 and 20 percent inulin (Celik and others 2013; Bornet 2008). The basic steps for extracting inulin from chicory root are as follows (Toneli and others 2010).

  In this study, the fact that inulin has low solubility at low temperatures was used to produce a concentrated solution. After evaporation the extract was frozen to -24⁰C, then thawed to 25⁰C, allowing for phase separation. The liquid phase was poured off, and the precipitate was spray dried. (Toneli and others 2010)

Inulin is composed of a glucose molecule linked via an α-(1, 2) linkage to a fructose molecule as in a sucrose molecule. The fructose molecule is then linked via a β-(2,1) linkage to repeating units of fructose which are also β-β-(2,1) linked (Causey and others 2000) (See Appendix A). Native inulin contains a mixture of oligomer and

Washing the root

Slicing/milling 

Extraction with hot water

Treatment with sulfur dioxide and lime

Filtering

Precipitation or Evaporation

of about 12. (González-Tomás and others 2009). According to this study, native inulin is subjected to partial enzymatic hydrolysis with the enzyme endo-inulinase, resulting in the production of oligofructose with a degree of polymerization (DP) of 2 to 7. To produce long chain inulin with a DP of 22-25, the oligomers are either filtered out using

ultrafiltration, or crystallized out using crystallization (González-Tomás and others 2009). The smaller the molecule the more soluble the molecule is in water (Tárrega and others 2010). The temperature affects the solubility of inulin in water; at 10⁰C

approximately 6%, 90⁰C approximately 35% (Silva 1996). The degree of polymerization of inulin is anywhere from 2-60. Differences in chain length result in different uses of the molecule. The function of inulin depends on the degree of polymerization. Inulin can be used in several different ways as a food additive, and also as a dietary supplement. As a food additive, it can be used as a fat replacer, sugar replacer, bulking agent or texturizing agent. As a dietary supplement, it functions as a prebiotic, soluble dietary fiber, increases the absorption of calcium, and lowers serum blood cholesterol (Causey and others 2000).

Type of Inulin Degree of Polymerization

Standard^a 2-60 units

High Performance^b ~25 units

Oligofructose^c ≤10 units

a.Polydisperse b.small weight oligomers have been removed c. enzymatic hydrolysis (Roberfroid 1999; Roberfroid and others 1993; Niness 1999)

2.3.1 FAT REPLACER  

Inulin has the ability to form a gel network with water which is the property that leads to its use as a fat replacer (Franck 2002). Greater than 25% concentration of inulin results in a gel formation that mimics the characteristics of fat (Zimeri and Kokini 2002).

The addition of hydrocolloids affects the gel formation of inulin in solution (Pszczola 1997). Inulin is a nondigestible polysaccharide that has characteristics that improve the mouthfeel of products; it was used in a frozen yogurt product, and the amount that was concluded to be desirable was 5% (El-Nagar and others 2002).

2.3.2 SUGAR REPLACER  

  Inulin can be used as a sugar replacer in dairy products, frozen desserts, fillings, fruit preparations, meal replacers, and chocolate (Franck 2002). The percentage of inulin used in the various applications differs, but in dairy products and frozen desserts it is suggested that the percentage should be 2-10 (% w/w). However, oligofructose powder is better suited for use as a sugar replacer since its average degree of polymerization (DP) is 4, compared with high performance inulin at 25 DP and standard inulin at 12 DP.

Oligofructose was 35 percent as sweet as sucrose (Franck 2002).   

2.3.3 DIETARY FIBER